<!DOCTYPE html>
<html>
	<head>
		<meta charset="UTF-8">
		<title></title>
	</head>
	<body>
	</body>
	<script type="text/javascript">
		var a = "42";
		var b = "0";
		
		var c = 42;
		var d = 0;
	
		var arr1 = [1,2];
		var arr2 = [3,4];

		
		console.log(a + b);// '420'
		console.log(c + d); //42

		// 先执行ToString规则
		console.log(arr1 + arr2); //"1,23,4"
		
	</script>
</html>
